Elongated electron-emission cathode assembly and method

ABSTRACT

This disclosure relates to generating an elongated electron beam curtain with the aid of an elongated tubular cathode structure transversely supported against sagging and distortion from a partially surrounding heat-reflecting thermal barrier channel support, particularly adapted for mounting with Pierce type or other beam-forming electrode structures.

United States Patent 11 1 Quintal et al.

ELONGATED ELECTRON-EMISSION CATHODE ASSEMBLY AND METHOD Inventors: Bertram S. Quintal, Peabody; Derek J. Maynard, Danvers, both of Mass.

Assignee: Energy Sciences 1nc., Burlington,

Mass.

Filed: Man-30, 1973 Appl. No: 346,324

Related [1.8. Application Data Division of Ser. No. 256,887. May 25 1972 Pat. No. 3,745,396.

us. 01. 313/346, 315/94 Int. Cl. H01 j 19/06 Field of Search 315/94; 313/346; 29/2514 References Cited UNlTED STATES PATENTS 12/1953 Espersen 29/25.14

K111i"; 315/94 Katz et al 313/346 Primary Exariiiner-Nathan Kaufman Attorney. Agent, or Firm-Rifles and Rines; Shapiro I and Shapiro 5 7 1 ABSTRACT This disclosure relates to generating an elongated electron beam curtain with the aid 01' an elongated tubular cathode structure transversely supported against sagging and distortion from a partially surrounding heat-reflecting thermal barrier channel support, particularly adapted for mounting with Pierce type or other beam-forming electrode structures.

3-Claims, 1 Drawing Figure 14 1 Nov. 12, 1974 ELONGATED ELECTRON-EMISSION CATHODE ASSEMBLY AND METHOD This is a division of application Ser. No. 256,887, filed May 25, I972, now Pat. No. 3,745,396, issued July 10, I973.

The present invention relates to electron-emission cathode assemblies and methods, being particularly, though not exclusively, concerned with the production of energetic electron beams of considerable length for such purposes as extended-dimension electron treating or processing through elongated electron gun windows and the like.

Cathodes of somewhat long dimensions have heretofore been constructed in filamentary form, either heated end-to-end, or composited by a plurality of short filaments transverse to the length of the electron gun, which is an application of standardly used electron tube cathode technique. Such devices, while useful in certain applications, are inherently seriously limited in practical length, are subject to serious lack of uniform emission densities therealong, and are difficult to form or transversely spread into an expanded uniform de- I the tubular member 2, or an external heater, or by a nisty beam as for projection through an elongated elec- A further object is to provide a novel electron-' emission cathode assembly and method that is particularly adapted for electron beam generation over very long previously unattained dimensions, say for more than centimeters to 200 centimeters, more or less, and that can achieve this result with electron optical expansion or spreading into uniform density beam curtains.

An additional object is to provide a novel electron cathode and gun assembly of more general utility, as well.

Other and further objects will be explained hereinafter and are more particularly delineated in the appended claims. In summary, however, from one of its aspects, the invention contemplates an electronemission cathode assembly having, in combination, an elongated tubular conductive member adapted to become heated to electron emission temperature and provided with a predetermined exposed external electronemissive wall surface; tubular thermal barrier and baffle means of larger cross dimension than the member, insulatingly spaced from and extending along and surrounding the other wall surfaces of the tubular member to reflect heat therefrom back thereto, but open to expose said predetermined wall surface thereof; and means comprising a plurality of supporting means extending transversely of the tubular thermal barrier and baffle means and the tubular member from which it is insulatingly separated, at regions spaced therealong, the supporting means being insulated from the walls of the tubular member. Preferred details are later set forth.

The invention will now be described with reference to the accompanying drawing, the single FIGURE of which is an isometric view illustrating the same in preferred form, with parts partially broken away to show details of construction.

Referring to the drawing, the cathode is illustrated generally at 2 in the form of an elongated longitudinal square or rectangular hollow tubular metal or other heat pipe at an end thereof, or otherwise, to bring the electron-emitting wall 2' to electron emission temperature.

Partially surrounding the tubular cathode member 2 on its sidewall portions 2" and upperwall portion 2" is a downwardly positioned open-bottom U-shaped tubular channel thermal barrier and baffle assembly comprising an inner conductive tubular channel 6 along the external walls of which thermal insulation 8 is disposed, and an outer U-shaped tubular channel 1. In preferred form, the thermal insulation 8 comprises multifoil layers of thin tantalum or tungsten and the like separated by high temperature dielectric material such as boron nitride and the like.

The inner surfaces of the sidewalls of the tubular channel 6 are shown isolated or separated by an insulator spacer 4 from the current-carrying side wall portions 2" of the tubular cathode 2, and the upper wall is space-insulated from the upper current-carrying wall portion 2" of the .cathode 2. The inner surfaces of the side walls of the outer tubular channel 1, at least in part, contact the thermal insulation layers 8, and are shown spaced thereabove at the upper wall. A plurality of supporting posts l617, positioned at successive locations longitudinally along the elongated cathode 2, support the cathode against sagging or other distortion in use (so common with the filamentary cathode approach) from the thermal barrier and baffle channel structure 1-8-6, with the posts themselves also being insulated from the current-carrying wall portions of the cathode 2 by the portion of the insulator 4 that extends transversely therethrough. By this construction, the thermal barrier structure may be maintained at ground or some other reference potential, with complete electrical isolation from the cathode 2.

In operation, it has been found that the heat generated from the sidewall portions 2" and upper wall portion 2" of the cathode 2 as the current passes therealong in the preferred embodiment, or as it is otherwise heated, is radiated within the thermal barrier and baffle channels 6-8-1 and becomes reflected back, further to intensify the heating and thus electron-emission of the exposed bottom wall portion 2', which may be coated externally with a low work function material.

Through this technique and structure, moreover, the cathode 2 is readily adapted for use in Pierce-type and other apertured electrode assemblies for field-shaping and beam forming and expanding purposes. The assembly is shown, indeed, suspended by supporting bolts 10 from an elongated U-channel structure 12-14 within which it is centered by guide pins 15 and to which correspondingly elongated Pierce-type electrodes 13 and 19, for example, may be conveniently attached below the cathode-emitting surface 2' and extending therealong. The electrode 13 is in the conventional knifeedge form, and the electrode 19 disposed therebelow and insulated therefrom by the spacer l8, defines the field-shaping aperture for expanding or spreading the cathode-emitted electrons into a uniform density, transversely wide, longitudinal electron beam curtain for covering an elongated, wide electron window or the like therebelow, schematically shown at W.

As an example, the substantially square cathode tube 2 may be of tantalum or tungsten, with the inner channel 6 also of tantalum and the outer channel 1 of lower temperature stainless steel. ln successful structures, the tube 2 has been about V4 inch on a side and about 42 inches long, with the outer channel 1 about 0.56 inch on the side. The supporting posts 16 may be of tungsten, and the insulation 4 of high-temperature dielectric boron nitride or the like. The cathode temperature may reach l,800 to 1 900C in operation, and even up to 2,200C if tungsten is used, all without sagging or other distortion or non-uniformity of emission area, and with the vastly improved efficiency stemming from the thermal barrier and baffle illumination of the cathode member 2 by forcing the heat to flow into the exposed bottom surface 2. Structures of this construction have been successfully so operated to expand the beam to times the initial inch width of the emitting surface 2. Through the use of the invention, indeed, one starts with an emitting surface 2 that can be a significant part of the transverse width of the ultimate window, and, indeed, has a significantly larger emitting area than filamentary cathodes, such that it can operate at a lower temperature than such filamerits. A suitable low work function coating material for the emitting surface 2 is lanthinum hexaboridc, which enables adequate emission current densities such as milliamperes per square centimeter and greater at relatively low temperatures of the order of l,4t)tlC.

As before stated, other geometries and orientations may be employed, as well as other types of cathode heating and thermal barrier baffling; all such being considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A method of producing an elongated cathodic electron emission, that comprises. heating the wall portions of a tubular conductive member to electronemission temperature, reflecting the heat radiated by all of the wall portions of the tubular member except one continuously back upon such wall portions exposing said one wall portion to emit electrons therefrom. preventing said tubular member from sagging and otherwise distorting under said heating and reflected heat to provide a substantially uniform elongated electron emission, and expanding such electron emission into a substantially uniform wider electron beam curtain,

2. A method as claimed in claim 1 and in which the tubular conductive member is heated by passing current directly therealong.

3. A method as claimed in claim 1 and in which the tubular conductive member is heated by supplying heat 

1. A method of producing an elongated cathodic electron emission, that comprises, heating the wall portions of a tubular conductive member to electron-emission temperature, reflecting the heat radiated by all of the wall portions of the tubular member except one continuously back upon such wall portions exposing said one wall portion to emit electrons therefrom, preventing said tubular member from sagging and otherwise distorting under said heating and reflected heat to provide a substantially uniform elongated electron emission, and expanding such electron emission into a substantially uniform wider electron beam curtain.
 2. A method as claimed in claim 1 and in which the tubular conductive member is heated by passing current directly therealong.
 3. A method as claimed in claim 1 and in which the tubular conductive member is heated by supplying heat thereto indirectly. 